ELECTRICAL
10.10
FAN MOTOR CURRENT
DRA
W
A current draw test provides a good indication of fan
motor condition. Worn or damaged fan motors will
draw morecurrent, which causesa reductioninblade
speed and reduced cooling.
Fan Motor
Connect ammeter
between Or/Blk leads
Or/Blk
Fan
Motor
Harness
Or/Blk
Brn
Ammeter
1. Disconnect the harness from the thermistor.
2. ConnectaDCammeterinbetweenthefan switch
harness wires as shown.
3. Be sure fan blade is free to rotate.
4. Turn ignition key and engine stop switch to “ON”
position. Read thecurrent drawon ammeterwith
fan running.
5. If the fan motor draws more than 7.5 Amps,
continuous, replace the motor.
Fan Motor Current Draw:
Less Than 7.5 Amps
TEMPERATURE SENSOR
(THERMISTOR) OPERATION
/
TEST
The thermistor relays a power signal to the ECM
dependingonenginecoolanttemperature.Shouldthe
thermistor fail open the engine Hot light and fan will
both comeon. Withengine cold, disconnectleadand
measure resistance of sensor between the two
Yellow/Blackconnectorterminals. Thereshouldbeno
continuity from the thermistor lead to engine ground.
See “Engine Temperature Controller” on Page 10.4
for additional information on thermistor operation.
SITUATION OHMS
READING
DIAGNOSIS /
ACTION
Hot light ON &
Fan ON
Above 50k Open Thermistor /
Replace Thermistor
Hot light ON Below 178 Engine Overheat
or Bad Thermistor
THERMISTOR READING DURING OPERATION
Condition
Approx. Reading
(Min--Max)
Temperature
Hot Light
On
178Ω -- 190Ω 215° F
(102° C)
Fan Off 296Ω -- 316Ω 180° F(82° C)
Fan On 236Ω -- 251Ω 195° F(91° C)
1. Placethermistorinawaterbathandthermometer
andsubmerseit tothebaseof thethreads.Donot
allow threads to contact container or inaccurate
reading will result.
2. Heat slowly and monitor the resistance at various
water temperatures with a thermometer or
Fluket meter pyrometer.
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